This invention relates to the automatic preparation of samples in vials or containers. More particularly, the invention relates to the automatic preparation of liquid samples in vials for use in a chemical analysis system.
Automation of chemical analyses which were once performed by hand has progressed significantly. In the field of liquid chromatography, a number of automated chromatographic analysis systems are currently commercially available. These systems, referred to as autosamplers, aid in the automation of chromatographic analysis by storing a number of individual samples and injecting them sequentially into a chromatograph for analysis. The chromatographic analysis, which typically takes between about 10 and 60 minutes, can be completed without human intervention.
Autosampler systems typically use trays of sample-containing vials of a small volume (e.g. 1.5-1.8 ml) which are fabricated of glass. The vials may be sealed with a flexible septum held onto the top of the vial by a cap with a hole in the center thereof. The hole exposes a portion of the rubber septum to a hollow needle which is pushed through the septum and into the sample.
Suction and/or pressure is used withdraw a predetermined amount of the sample through the needle, and the sample is then injected into the chromatograph. In early autosamplers, a syringe was used to withdraw the sample by suction into a sample loop, and then used to discharge the sample therefrom by pressure for analysis. It is a common problem in all autosamplers that the accuracy of sample delivery may be affected by loss of sample in wetting the sides of the sample loop, and the precision with which samples are obtained may be similarly limited by the syringe, which is sized to handle both large and small volumes.
Currently, additional demands are being placed on such autosampler systems to increase further the automation of the chemical analyses. In addition to automated sampling there is the desire to produce systems capable of some sample preparation. For example, there may be a need to dilute the sample before analysis or to add a reagent to aid in sample detection. Some reagents may take several minutes to react and may require continuous mixing and/or heating at elevated temperatures. As this time is comparable to the time required for chromatographic analysis, it may be desirable to have more than one sample in process at one time. It may also be necessary to remove a sample from the tray and perform an operation on it such as mixing or heating, or simply to provide the sample to one of various analysis stations.
Autosamplers of more recent vintage still perform the same basic tasks, but incorporate various apparatus and method improvements to improve sampling precision and accuracy, and to increase the capability for sample preparation. For example, Nohl et al, U.S. Pat. No. 4,957,009 (the '009 patent) discloses a pushloop liquid sampling method for an existing sampling apparatus which improves accuracy of sample delivery by eliminating mechanical backlash in the syringe drive mechanism. Stone, U.S. Pat. No. 4,713,974 (the '974 patent) shows a variety of improvements in an autosampler apparatus which increase its capability for preparing samples and quickly flush or prime the lines. However, the need for manual priming and solvent delivery in accordance with the '974 patent, prevents automatic operation. As well, it remains a problem in both the '974 and '009 patents that the accuracy of sample delivery may be affected by loss of sample in wetting the sides of the sample tube, and the precision with which samples are obtained may be limited by the syringe size The '974 patent suggests manual interchange of syringes having different capacities to change the capacity, precision and accuracy of sample preparation. However, the need for operator intervention to perform such procedures again inhibits truly automatic sample preparation.
Accordingly, there is a need in the art for an autosampler which is capable of automatic operation to provide sample preparation with improved accuracy and precision.